It is well established that the measure of peak expiratory flow rate is a good indication of the condition of the airways of the body. Thus, such measurement is helpful, for example, in the management of asthma.
Asthma is recognized as a chronic disease which can manifest itself in bronchial inflammation of which the patient may be unaware, and has the ability to result in an acute attack under a variety of circumstances, resulting in the partial or complete obstruction of the breathing of the individual. Because of its chronic nature, asthma patients must be continuously on guard to become aware of symptoms which might forebode an attack. The use of effective anti-asthma drugs can substantially limit or eliminate such attacks, but need to be dispensed with care to prevent both over- and under-dosing.
An effective method for managing asthma is testing the respiratory function. Such testing may typically be performed by the patient himself by use of a portable peak expiratory flow meter. Such devices measure the peak expiratory flow rate, that is, the maximum rate of air flow which can be exhaled under various circumstances and at various times throughout the day. This permits the patient to monitor the respiratory function and receive warning of changes in respiratory function which may indicate an impending asthma attack.
Typically, such peak flow meters, even when characterized as "portable" are of relatively large size, and are not conducive to inconspicuous transport or use by the patient. The peak flow meter depicted in Alvino, U.S. Pat. No. 4,944,306, for example, utilizes a vertically-extending indicator tube affixed to a horizontal mouthpiece/exit port. While providing accurate peak flow rate measurement over a range of expiratory flows, such an apparatus is relatively large and cumbersome, and is not easily transported on the person. Such constructions limit the effectiveness and usefulness of such devices by impeding the ability of the patient to keep such a peak flow meter with him at all times so that respiratory rate can be monitored whenever required.
It is thus a purpose of the present invention to provide a peak flow meter of improved construction which results in a compact unit being able to be carried on the person.
Yet another purpose of the present invention is to provide a peak flow meter having the capacity to be folded into a compact unit for transit and being able to be unfolded into a use position.
Still another purpose of the present invention is to provide such a device in which the mouthpiece of the unit is protected from the environment when not in use, thus improving the sanitation and safety of the unit.
Yet a further purpose of the present invention is to provide such a device in a manner which may be efficiently and economically manufactured.